Invasive procedures are often required for accurate screening and diagnosis of common medical conditions (Boolchand et al, Ann. Intern. Med. 145:654-659 (2006)). Examination of the peripheral blood often suffices to establish certain diagnoses, such as chronic lymphocytic leukemia (Damle et al, Blood Epub Ahead of Print (2007)), which afflicts the circulating lymphocyte directly. Measurement of total white blood cell counts and the WBC differential (e.g. neutrophils, lymphocytes, monocytes) is routinely performed in medical practice and can facilitate many diagnoses (e.g. bacterial or viral infection). Recently, it has been suggested that gene expression profiling of peripheral blood cells, particularly lymphocytes, can serve as sensitive tool to assess for the presence of certain diseases, such as systemic lupus erythematosus, rheumatoid arthritis, neurologic disease, viral and bacterial infections, breast cancer, atherosclerosis and environmental exposures, including tobacco smoke (Mandel et al, Lupus 15:451-456 (2006), Heller et al, Proc. Natl. Acad. Sci. USA 94:2150-2155 (1997), Edwards et al, Mol. Med. 13:40-58 (2007), Baird, Stroke 38:694-698 (2007), Rubins et al, Proc. Natl. Acad. Sci. USA 101:15190-15195 (2004), Martin et al, Proc. Natl. Acad. Sci. USA 98:2646-2651 (2001), Patino et al, Proc. Natl. Acad. Sci. USA 102:3423-3428 (2005), Lampe et al, Cancer Epidemiol. Biomarkers Prev. 13:445-453 (2004), Ramilo et al, Blood 109:2066-2077 (2007)). Results from these studies suggest that patterns of gene expression within circulating PB cells can distinguish individuals afflicted by these conditions from those who are not (Mandel et al, Lupus 15:451-456 (2006), Heller et al, Proc. Natl. Acad. Sci. USA 94:2150-2155 (1997), Edwards et al, Mol. Med. 13:40-58 (2007), Baird, Stroke 38:694-698 (2007), Rubins et al, Proc. Natl. Acad. Sci. USA 101:15190-15195 (2004), Martin et al, Proc. Natl. Acad. Sci. USA 98:2646-2651 (2001), Patino et al, Proc. Natl. Acad. Sci. USA 102:3423-3428 (2005), Lampe et al, Cancer Epidemiol. Biomarkers Prev. 13:445-453 (2004), Ramilo et al, Blood 109:2066-2077 (2007)). It has, therefore, been suggested that PB gene expression profiling has potential utility in the screening for diseases and environmental exposures.
Any consideration of applying PB gene expression profiles for the detection of disease or environmental exposures requires a determination of the impact of PB cellular composition, time, gender, and genotype on PB gene expression (Lampe et al, Cancer Epidemiol. Biomarkers Prev. 13:445-453 (2004), Ramilo et al, Blood 109:2066-2077 (2007), Whitney et al, Proc. Natl. Acad. Sci. USA 101:1896-1901 (2003), Yan et al, Science 297:1143 (2002)). Additionally, it is unclear whether PB gene expression profiles that have been associated with various medical conditions are specific for that phenotype, or rather reflect a generalized response to genotoxic stress. Examination of the specificity of PB gene expression profiles in response to different stimuli and the durability of these signatures over time is critical to the translation of this strategy into clinical practice.
Ionizing radiation represents a particularly important environmental hazard, which, at lowest dose exposures, causes little acute health effects (Kaiser, Science 302:378 (2003)) and, at higher dose exposures, can cause acute radiation syndrome and death (Wasalenko et al, Ann. Int. Med. 140:1037-1051 (2004), Mettler et al, N. Engl. J. Med. 346:1554-1561 (2002), Dainiak, Exp. Hematol. 30:513-528 (2002)). Numerous studies have been performed to attempt to understand the biologic effects of ionizing radiation in humans. Specific mutations in p53 and HPRT have been identified in somatic cells from survivors of the Hiroshima and Nagasaki atomic bombings (Iwamoto et al, J. Natl. Canc. Inst. 90:1167-1168 (1998), Hirai et al, Mutant Res. 329:183-196 (1995), Takeshima et al, Lancet 342:1520-1521 (1993), Neel et al, Annu. Rev. Genet. 24:327-362 (1990)).
Gene expression analyses have been performed on human tumor cells, cell lines, and peripheral blood from small numbers of irradiated patients in order to identify specific genes that are involved in the response to radiation injury (Jen et al, Genome Res. 13:2092-2100 (2003), Amundson et al, Radiat. Res. 154:342-346 (2000), Amundson et al, Radiat. Res. 156:657-661 (2001), Falt et al, Carcinogenesis 24:1837-1845 (2003), Amundson et al, Cancer Res. 64:6368-6371 (2004)). Recently, public health focus has centered on the development of capabilities to accurately screen large numbers of people for radiation exposure in light of the anticipated use of radiological or nuclear materials by terrorists to produce “dirty bombs” or “improvised nuclear devices” (Wasalenko et al, Ann. Int. Med. 140:1037-1051 (2004), Mettler et al, N. Engl. J. Med. 346:1554-1561 (2002), Dainiak, Exp. Hematol. 30:513-528 (2002)).
A method of screening humans for environmental exposure has been suggested. This method relies on the identification of patterns of gene expression, or metagenes in PB cells that accurately distinguish between irradiated and non-irradiated individuals (Dressman et al, PLoS Med. 4:690-701 (2007)). Metagenes can be identified in the PB that distinguish different levels of exposure with an accuracy of 96% (Dressman et al, PLoS Med. 4:690-701 (2007)).
The present invention results, at least in part, from studies designed to evaluate the specificity of PB gene expression signatures and to determine the influence of genetic variation and time on the performance of the signature. The results of these studies indicate that this approach represents a viable strategy for identifying environmental exposures and one that can be employed for screening populations of affected individuals.